Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Functional Electrical Stimulation (FES) systems such as the Freehand system by NeuroControl (Cleveland, Ohio) have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Each of these implantable neurostimulation systems typically includes one or more therapy delivery elements implanted at the desired stimulation site and an implantable neurostimulator, such as an implantable pulse generator (IPG), implanted remotely from the stimulation site, but coupled either directly to the therapy delivery elements or indirectly to the therapy delivery elements via one or more extensions in cases where the length of the therapy delivery elements is insufficient to reach the IPG. Electrical pulses can be delivered from the neurostimulator to the therapy delivery elements to stimulate the tissue and provide the desired efficacious therapy to the patient.
In the context of an SCS procedure, one or more therapy delivery elements are introduced through the patient's back into the epidural space under fluoroscopy, such that the electrodes carried by the leads are arranged in a desired pattern and spacing to create an electrode array. The specific procedure used to implant the therapy delivery elements will ultimately depend on the type of therapy delivery elements used. Currently, there are two types of commercially available therapy delivery elements: a percutaneous lead and a paddle lead.
A percutaneous lead includes a cylindrical body with ring electrodes, and can be introduced into contact with the affected spinal tissue through a Touhy-like needle, which passes through the skin, between the desired vertebrae, and into the epidural space above the dura layer. For unilateral pain, a percutaneous lead is placed on the corresponding lateral side of the spinal cord. For bilateral pain, a percutaneous lead is placed down the midline of the spinal cord, or two percutaneous leads are placed down the respective sides of the midline. In many cases, a stylet, such as a metallic wire, is inserted into a lumen running through the center of each of the percutaneous leads to aid in insertion of the lead through the needle and into the epidural space. The stylet gives the lead rigidity during positioning, and once the lead is positioned, the stylet can be removed after which the lead becomes flaccid.
Paddle leads have a paddle-like configuration and typically possess multiple electrodes arranged in one or more independent columns. Paddle leads provide a more focused energy delivery than percutaneous leads because electrodes may be present on only one surface of the lead. Paddle leads may be desirable in certain situations because they provide more direct stimulation to a specific surface and require less energy to produce a desired effect. Because paddle leads are larger than percutaneous leads, they have historically required surgical implantation through a procedure known as partial laminectomy that requires the resection and removal of vertebral tissue.
Paddle leads have limited torsional stiffness and bending rigidity. As a result, physicians use various dissection tools to open a space in the tissue prior to attempting to implant paddle leads at the desired site. The dissection tool must have sufficient stiffness to open the tissue, while not creating excess pressure on the spinal cord or nerve roots. After the space is opened a second tool or blank is then typically inserted to verify that the space created is sufficient to accommodate the paddle lead.
Even with a space formed in the tissue to accept the paddle lead, paddle leads are difficult to manipulate and control as they are directed to their intended implantation site. As a result, surgeons typically create a space in the tissue greater than the size of the paddle lead to aid in implantation. The oversize space, however, results in imprecise positioning and subsequent migration of the paddle lead within the patient.